Multi‐resonant thermally activated delayed fluorescent (MR‐TADF) materials are blooming for high‐resolution organic light‐emitting diodes (OLEDs). However, boron/nitrogen (B/N)‐integrated MR‐TADF emitters suffer severe efficiency roll‐off from their strong inter‐molecular π–π interactions. Herein, versatile narrowband pure blue emitters (mono‐mx‐CzDABNA and tri‐mx‐CzDABNA) are demonstrated featuring a ring‐fused extended π‐skeleton: a classic steric hindrance and rigidity accessed by integrating with meta‐xylene (mx) rotors. tri‐mx‐CzDABNA shows a narrowband (FWHM, 26 nm) pure blue emission (λmax, 462 nm) with substantial hypsochromic shift (12 nm) while maintaining MR‐TADF characteristics. The key solid‐state analyses conclude that they conceivably suppress the non‐radiative energy loss, thus improving the photoluminescence quantum yield (PLQY > 90%) and rate of reverse intersystem crossing (RISC) (kRISC ≈2.85 × 105 s−1). The integration of tri meta‐xylene significantly leads to an enhanced horizontal dipole ratio (HDR) from 65% to 85%. Hyperfluorescent‐OLEDs are fabricated using designed MR‐TADF as terminal emitter, achieving a narrowband (FWHM, 34 nm) pure blue electroluminescence (λmax, 472 nm) and maximum external quantum efficiency (EQEmax) of 26.97% with magnificently suppressed efficiency roll‐off (7.8%) at 1000 cd m−2. So, it is believed that regulation of internal efficiencies and high color purity can amplify the route to achieving a narrowband pure blue emission through new synthetic MR‐TADF approaches.

The widespread use of Internet-of-things (IoT) devices has inspired researchers to adopt unique material design strategies to realize efficient indoor organic photovoltaic (OPV) systems. However, despite acceptor halogenation being an effective strategy for modulating OPV properties, studies on the systematic examination of nonfullerene acceptor- (NFA-) OPVs under dim indoor light using the halogenation approach are scarce. This study evaluates the performance of NFA-OPVs under indoor light by employing a halogenation approach with Y6-derivatives. The choice of the chlorination or fluorination unit in an NFA significantly affects the indoor performance of OPVs. The champion OPV devices with a chlorinated acceptor demonstrated excellent power conversion efficiency (PCE) of 25.5% compared to that of the fluorinated acceptor (PCE: 22.5%) under 1000-lx light-emitting-diode (LED) illumination. Moreover, suitable energy levels, satisfactory spectral matching, and improved surface morphology of the chlorinated acceptors resulted in the excellent indoor performance of the OPVs. In addition, acceptor chlorination resulted in high crystallinity and planarity, which facilitated suppressed trap-assisted recombination and low open-circuit voltage (VOC) loss of OPV devices in an indoor environment.

Herein, we design and characterize 9-heterocyclic ring non-fullerene acceptors (NFAs) with the extended backbone of indacenodithiophene by cyclopenta [2,1-b:3,4-b’] dithiophene (CPDT). The planar conjugated CPDT donor enhances absorption by reducing vibronic transition and charge transport. Developed NFAs with different end groups shows maximum absorption at approximately 790–850 nm in film. Because of the electronegative nature of the end-group, the corresponding acceptors showed deeper LUMO energy levels and red-shifted ultraviolet absorption. We investigate the crystallinity, film morphology, surface energy, and electronic as well as photovoltaic performance. The organic photovoltaic cells using novel NFAs with the halogen end groups fluorine or chlorine demonstrate better charge collection and faster exciton dissociation than photovoltaic cells using NFAs with methyl or lacking a substituent. Photovoltaic devices constructed from m-Me-ITIC with various end groups deliver power conversion efficiencies of 3.6–11.8%.